Comparing Through-the-Needle With Suture-Method Catheter Designs for Popliteal Nerve Blocks: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparing Through-the-Needle With Suture-Method Catheter Designs for Popliteal Nerve Blocks (NCT03442036), a randomized na study. The primary outcome is Average Pain.

2. Clinical Question

The trial description frames the comparison as an assessment of the relative risks and benefits of these two catheter designs for postoperative analgesia. The primary endpoint addresses reported pain, while opioid consumption and worst pain are listed as secondary outcomes. The primary result therefore speaks to average pain over the specified postoperative period; it does not, by itself, summarize every outcome relevant to catheter use or postoperative care.

3. Trial Design

The registry describes a randomized, observer-masked, controlled, parallel-arm clinical trial comparing through-the-needle and suture-method perineural catheter designs for continuous popliteal-sciatic nerve blocks. The masking field is recorded as double. The record does not specify who was masked or how masking was implemented, so those details are not reported in the registry record.

The trial enrolled 70 participants, with 35 assigned to each catheter-design group in the posted primary outcome results. The trial status is completed. The recorded start date is 2018-04-06, and the primary completion date is 2019-04-01. The phase is listed as NA. The sponsor is the University of California, San Diego.

In the through-the-needle group, the catheter was inserted through a straight hollow-bore needle. In the suture-method group, the catheter was attached to a hollow suture-shaped needle that pulled it adjacent to the target nerve. Both descriptions say that local anesthetic was infused through the catheter to provide postoperative pain control.

The primary outcome was average pain, expressed as a mean and standard deviation, over the first two postoperative days combined. The record also lists opioid consumption and worst pain as secondary outcomes. It reports four outcome measures in total, while two secondary outcomes are posted. Details such as eligibility criteria, the allocation procedure, the original sample-size justification, and the protocol’s planned statistical analyses are not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Average Pain, measured over first two postoperative days combined.

The primary endpoint is average pain across the first two postoperative days combined. Pain was assessed using a numeric rating scale whose anchors are 0 for no pain and 10 for worst imaginable pain. The posted group summaries are means with standard deviations, so the primary comparison concerns average scores rather than the proportion of participants above or below a particular pain threshold.

A mean offers a concise description of the group’s scores across the specified period. The standard deviation describes how dispersed individual scores were around that group mean. These answer different questions: the mean describes the average level, while the standard deviation describes variation among participants. Neither alone shows the full distribution of scores or how many participants had especially high or low pain ratings.

Average pain is relevant to the trial’s stated purpose because the catheter designs were being compared in the context of postoperative analgesia. The endpoint is limited to reported pain over the combined postoperative period. It does not directly measure catheter placement success, duration of analgesia, opioid use, or adverse events. Opioid consumption and worst pain appear as secondary outcomes, but detailed results for those outcomes are not included in the primary comparison.

7. Results Posted in the Registry

• Suture-Method Technique: mean 3.40 versus 2.70 on control; difference 0.70 (95% CI -0.42 to 1.82), standardized effect d = 0.29; z-test p = 0.222.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: each participant’s pain rating is represented on a numeric scale, and the group results are summarized by means and standard deviations. A mean is the arithmetic average of the observed scores. A standard deviation describes the typical spread of observations around that average. It is not the uncertainty in the estimated mean, and it is not a range containing all participants’ scores.

The comparison is reported as a mean difference, with the suture-method group compared against the through-the-needle group. The registered summary gives means of 3.4 and 2.7, respectively, and a mean difference of 0.7. The direction depends on this ordering: a positive value means the suture-method group had the higher average score in the posted results. Reversing the order would reverse the sign, even though the underlying group summaries would be unchanged.

An interval around an estimated difference expresses uncertainty about the range of values compatible with the data under the method used to construct it. The posted interval crosses zero. Zero represents no difference between the group means under the stated comparison. Because the interval also extends to either side of zero, the data do not pin down the direction of the underlying mean difference with high precision. The confidence level and construction method for this interval are not reported in the registry record, so they should not be inferred from the endpoints alone.

The unadjusted p-value is 0.222. In general, a p-value describes how unusual data at least as discrepant as those observed would be under a specified null model, assuming the model and its assumptions apply. It is not the probability that the null hypothesis is true, and it does not quantify the size or clinical importance of a difference. The registry does not report the complete analysis plan or confirm what inferential procedure produced this p-value. The value is explicitly unadjusted, so no adjustment for multiple comparisons is represented by it.

The posted comparison includes 35 participants in each group. Equal group counts are consistent with the reported allocation, but the registry record does not give details of the randomization sequence, concealment, or the handling of participants after assignment. Although the trial is described as randomized and the masking field is double, operational details of those procedures are not reported in the registry record.

Planning illustrations based on the observed effect use a two-sided significance level of 0.05, equal allocation between the groups, and a normal approximation. They consider the stated effect and smaller fractions of that observed effect. Such calculations answer a planning question: under the stated assumptions, how many participants per arm would be needed for a chosen probability of detecting the specified effect? They do not describe the trial’s original design unless the registry confirms those were its assumptions, and the original design assumptions are not reported.

Power in this planning context is the probability of rejecting a null hypothesis under a specified alternative, when the assumptions used in the calculation hold. The 80% and 90% columns correspond to different planned probabilities of detecting the stated effect. They are not probabilities that the result is correct, and they do not measure the quality of the observed estimate. The figures are planning illustrations based on the observed effect, not observed power.

Smaller target effects require more participants under otherwise unchanged assumptions because a smaller separation between group means is harder to distinguish from random variation. The planning figures therefore rise as the target fraction of the observed effect becomes smaller. These calculations use a normal approximation and assume equal allocation; they do not incorporate unreported design features, missing observations, or other aspects of the trial’s original plan.

For continuous outcomes, standard deviation matters to planning because greater variability makes a given difference harder to distinguish from noise. The posted standard deviations are 2.4 in both groups. In general, if the outcome distribution is highly skewed or has unusual features, a normal approximation may not reflect the actual analysis well. The registry record does not report diagnostic checks, transformations, covariate adjustment, or an alternative model, so no claim can be made about whether such methods were used.

The record reports four outcome measures, identifies average pain as primary, and names opioid consumption and worst pain as secondary outcomes. It does not report the full analysis hierarchy, multiplicity strategy, missing-data method, or analysis population. Those omissions limit the ability to assess how the primary result fits into a prespecified set of analyses. A posted unadjusted p-value should therefore be interpreted as the reported result for this comparison, not as a complete account of all inferential decisions.

10. Confidence Intervals and Precision

The mean difference is 0.7 score points, with the suture-method group higher on average in the posted comparison. The reported interval extends below zero and above zero. This breadth across the no-difference value indicates that the estimate does not sharply distinguish a positive difference from no difference or a difference in the opposite direction. The interval’s endpoints are not repeated; its confidence level and calculation method are not reported in the registry record.

Precision concerns the uncertainty around an estimate, not whether an estimate is important. The interval provides more information about uncertainty than the point estimate alone: the point estimate is one value, whereas the interval represents a range of values compatible with the data under its statistical procedure. Since that range includes zero, the result does not exclude no mean difference. Since it also includes values on either side of zero, it does not establish the direction of a possible underlying difference.

The group means were 2.7 and 3.4, and the standard deviation was 2.4 in each group. These summaries show that scores varied within groups as well as differing in their averages. They do not reveal the detailed distribution or identify whether a subset of participants had scores that differed substantially from the group average.

The p-value of 0.222 is an unadjusted result and should not be treated as a measure of precision or effect size. The mean difference describes the estimated magnitude, while the interval describes uncertainty around that estimate. The registry does not provide the confidence level, interval method, or complete analysis plan, which limits further evaluation of precision.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. They assume a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each planning row uses the stated fraction of the observed effect as the effect to detect. The original sample-size assumptions for the trial itself are not reported in the registry record.

The 80% power column gives the number of participants per arm calculated to provide an 80% chance of detecting the specified effect under those planning assumptions. The 90% power column gives the corresponding number per arm for a 90% chance. A higher planned probability of detecting the effect requires more participants under the same assumptions. These are hypothetical design calculations based on the observed effect and its stated fractions; they are not observed power.

The rows consider planning for 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. The associated figures are 185 and 248 participants per arm for 100% of the observed effect; 329 and 440 for 75%; and 739 and 989 for 50%, for 80% and 90% power respectively. The pattern illustrates that smaller effects need more participants to detect under otherwise unchanged assumptions.

These values are planning illustrations, not evidence that the trial enrolled enough participants for a particular target or that a particular effect was detectable in the completed trial. They do not replace the registry’s unreported original sample-size justification, and the listed assumptions do not establish the full analysis plan.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = 0.700; pooled standard deviation σ = 2.400.
2. n = 2 × (1.96 + 0.842)² × 2.400² / 0.700² = 184.5, rounded up to 185 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- 0.7                      # observed difference in means
sigma <- 2.4                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(3442036)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 185 (80% power), 248 (90% power)
 75% of observed effect: n per arm = 329 (80% power), 440 (90% power)
 50% of observed effect: n per arm = 739 (80% power), 989 (90% power)
power.t.test: 185.5 
Simulated power at n = 185 per arm: 0.797 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry identifies average pain as the primary outcome and lists opioid consumption and worst pain as secondary outcomes. It also records four outcome measures in total, two posted secondary outcomes, and zero posted analyses. These entries do not provide a complete account of which outcomes were analyzed, which comparisons were prespecified, or how results were selected for reporting.

Multiplicity arises when several outcomes, time points, or comparisons are tested. In general, conducting more tests can increase the chance of at least one apparently unusual result even when no underlying effect exists. Statistical procedures can address this issue, but the registry record does not report whether any multiplicity adjustment was planned or used. The primary comparison’s p-value is described as unadjusted, so it should not be interpreted as reflecting an adjustment for other analyses.

The record does not state how missing pain scores were handled, whether all randomized participants contributed to the primary outcome, or whether analysis followed assignment regardless of catheter use. The number of participants in the posted primary summaries is 35 in each group, but that alone does not establish the analysis population or the completeness of outcome data. The missing-data approach and analysis populations are not reported in the registry record.

Other details that would help evaluate the inferential results are also absent, including the full statistical analysis plan, the confidence-interval level and construction method, and whether adjustment for baseline variables or other covariates was used. These gaps do not invalidate the posted summaries, but they limit assessment of whether the reported analysis followed a prespecified plan and how robust it may be to analytic choices.

14. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: deep vein thrombosis (2.9%).

The serious adverse event summaries list 35 participants at risk in each group. The through-the-needle group had zero participants affected by serious adverse events, and the registry-listed Suture-Catheter group had one participant affected. Deaths were recorded as zero in both groups. The top serious-event term listed is deep vein thrombosis, with a value of 2.9%.

The adverse-event label Suture-Catheter differs from the Suture-Method Technique label used for the primary outcome arms. The registry does not explain that naming difference, so the labels should be kept distinct when describing the posted safety entry. The serious-event summaries report counts of participants affected, not a detailed account of event timing, duration, severity beyond the serious classification, or relatedness to the catheter design.

These figures are descriptive. A small number of events provides limited information for comparing safety between groups, and zero recorded deaths does not imply that every other type of harm was absent. The registry record does not provide the full adverse-event profile, event definitions, or methods used to assess causality. The safety entries should therefore be interpreted narrowly as the posted serious-event and death counts.

15. What the Result Does, and Does Not, Mean

The posted primary outcome shows average pain scores of 2.7 for the through-the-needle design and 3.4 for the suture-method design over the first two postoperative days combined. The mean difference was 0.7, with the suture-method group higher. The reported interval crosses zero, and the unadjusted p-value was 0.222. The estimate is therefore uncertain about the direction and size of any underlying difference.

This result does not demonstrate that the catheter designs are equivalent. Equivalence requires a prespecified margin and an analysis showing that plausible differences lie within that margin; no such margin or equivalence analysis is reported in the registry record. Nor does the result establish that one design is superior. The observed difference is a group-average estimate, not a guarantee about the experience of an individual participant.

The endpoint covers average pain across a combined postoperative period. It does not answer every question about postoperative analgesia, including opioid consumption, worst pain, or safety. Although opioid consumption and worst pain are listed as secondary outcomes, their detailed numerical findings are not included in the primary comparison. The serious adverse event entries are limited counts and do not establish a comprehensive safety comparison.

The trial was randomized and parallel-arm according to the registry, but details of randomization, masking implementation, missing-data handling, and the analysis population are not reported. The record also does not report the original sample-size justification or a full statistical plan. These limitations matter when considering how much weight to place on the estimate and whether it addresses a prespecified clinical question as planned.

The result is best understood as an imprecise comparison of posted group averages in this trial’s stated surgical and nerve-block context. It should not be generalized to settings or outcomes that the record does not describe, and it should not be interpreted as medical advice.

16. Why This Trial Matters Statistically

This trial presents a useful statistical distinction between an observed difference and the certainty with which that difference is estimated. The average pain scores differed by 0.7 points in the posted groups, but the interval crosses zero. A point estimate alone could suggest a direction; the interval makes clear that the estimate remains compatible with more than one direction.

The group standard deviations, each 2.4, provide context for the mean comparison by describing variation among participants. Clinical trial results are not determined solely by the difference between group averages: uncertainty also depends on how variable the outcome is and how much information the study contributes. The planning illustrations make this relation visible by showing how the required number per arm increases when the target effect is smaller.

The planning figures also underscore the distinction between retrospective illustrations and an original design justification. They use the observed effect and specified assumptions, but the registry does not report whether those assumptions guided the trial’s enrollment. Treating such figures as proof of adequate design or as observed power would conflate a hypothetical planning calculation with the completed trial’s actual design.

Finally, the record identifies multiple outcomes while leaving important analysis details unreported. Knowing which outcome is primary helps focus interpretation, but a complete statistical assessment also depends on multiplicity procedures, missing-data methods, analysis populations, and the prespecified plan. The available results support a bounded reading of this comparison rather than a broad conclusion about all outcomes or catheter performance.

17. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The registry record gives limited detail about participant eligibility, baseline characteristics, randomization procedures, allocation concealment, and implementation of masking. Although the trial is described as randomized and the masking field is double, the record does not specify who was masked or how. These omissions restrict evaluation of the trial’s conduct and of the groups’ comparability beyond the posted assignment and summaries.

The primary outcome is reported for the first two postoperative days combined. No separate time-specific primary summaries are included in the registry record for this comparison. A combined average may not show whether pain changed over time, and the group means and standard deviations do not reveal the full score distributions or individual patterns.

The record does not report the trial’s original sample-size justification, full statistical analysis plan, confidence-interval method or level, missing-data handling, or analysis populations. It also does not clarify the relationship between the listed outcome measures, posted secondary outcomes, and zero posted analyses. The unadjusted p-value cannot therefore be placed in a fully documented analysis hierarchy.

Safety information is limited to serious-event counts, deaths, and a listed serious-event term. The different Suture-Catheter label in the adverse-event group is not reconciled with the Suture-Method Technique label used for the primary outcome. Details about event timing, attribution, and the broader adverse-event profile are not reported in the registry record.

The trial addresses catheter designs in the context of postoperative analgesia after foot and ankle surgery. The registry record does not establish how these findings apply to other procedures, settings, or patient groups. These limitations counsel against drawing conclusions beyond the outcome and trial context described.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Comparing Through-the-Needle With Suture-Method Catheter Designs for Popliteal Nerve Blocks — NCT03442036.
• Registry record last updated 2021-02-17; status last verified 2021-01.
• Results first posted 2020-03-12.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

21. Record Summary

The registry describes a completed randomized, observer-masked, controlled, parallel-arm trial comparing through-the-needle and suture-method perineural catheter designs for continuous popliteal-sciatic nerve blocks after foot and ankle surgery. Enrollment was 70, with 35 participants in each group in the posted primary outcome results.

The primary outcome was average pain over the first two postoperative days combined, measured on a numeric rating scale from 0 to 10. Group means were 2.7 for through-the-needle and 3.4 for suture-method. The mean difference was 0.7, with an interval crossing zero and an unadjusted p-value of 0.222.

The registry lists opioid consumption and worst pain as secondary outcomes. Serious adverse events affected zero participants in the through-the-needle group and one in the Suture-Catheter group; deaths were zero in both groups. The original sample-size justification, full statistical plan, and several analysis details are not reported in the registry record.